A known ink jet printer as an example of a liquid droplet ejection device uses a so-called station supply system. The ink jet printer has a recording head, a sub-tank communicating with the recording head, and a carriage configured to reciprocate. The ink jet printer is configured to mount an ink cartridge. The ink jet printer is configured such that the carriage mounts thereon the recording head and the sub-tank, and the ink cartridge communicates with the sub-tank only when ink needs to be supplied from the ink cartridge to the sub-tank. In the other timing (when the ink needs not to be supplied from the ink cartridge to the sub-tank), the ink cartridge does not communicate with the sub-tank, and the ink cartridge and the sub-tank are separated from each other. Accordingly the ink is supplied from the ink cartridge to the sub-tank intermittently (e.g., see JP-A-2004-181952).